the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Climatological occurrences of hail and tornado associated with mesoscale convective systems in the United States
Abstract. Hail and tornadoes are hazardous weather events that are responsible for significant property damage and economic loss world-wide. The most devastating hail and tornado events are commonly produced by supercells in the United States. However, some hazard-producing supercells may grow upscale into mesoscale convective systems (MCSs) or may be embedded in MCSs. Quantifying the relationship of hail and tornado occurrences with MCSs on the long-term climatology is lacking. In this work, the radar features associated with MCSs are extracted from a 14-year MCS tracking database over the contiguous United States, and the hazard reports are matched to the extracted MCS features. We analyze the characteristics of hail and tornadoes associated with MCS characteristics and consider the seasonal and regional variabilities. On average, about 8–17 % of hail and 17–32 % of tornado events are associated with MCSs depending on various criteria used to define MCSs. The maximum total and MCS-associated hazard events occur in March–May, but the highest MCS-associated portion (23 % for hail and 45 % for tornado) occurs in winter (December–February) because MCS is the dominant type of convection due to strong synoptic forcing. In contrast to the decreasing trend in the relationship of MCS-associated fraction with hailstone size, the more severe the tornado event is, the more likely it is associated with an MCS. The different trends indicate the distinct mechanisms for the MCS-associated production of the two types of hazards.
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Jingyu Wang et al.
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RC1: 'Comment on nhess-2023-16', Anonymous Referee #1, 11 May 2023
Review of: “Climatological occurrences of hail and tornado associated with mesoscale convective systems in the United States”
Summary: The authors use collocated ground based radar MCS features and geostationary satellite tracked MCSs to follow MCSs over the United States throughout their lifetimes and define their life stage. Collocated observations of hail and tornadoes are collocated to each MCS to study the climatological occurrence of MCS produced severe hail and tornadoes on a monthly and per lifecycle stage basis. These are also compared with observed hail and tornadoes from all events to determine the percent contribution to the occurrence of these hazards by MCSs. The paper is well written and thorough, and, for the most part, logically organized. It would benefit from clarification of a few points and additional discussion of the methods used. I therefore recommend minor revisions.
General Comments:
- The methods section is lacking in a few key details, mostly descriptions of the datasets. This section should be expanded to include more technical details about how the datasets used are produced and how the derived quantities are defined. Specific examples are provided in the Specific Comments section.
- The introduction feels a bit jumbled and tends to jump from discussing hail to tornadoes and back within the same paragraph. It would read more smoothly and thus make the points of the introduction better if it were reorganized to discuss the findings of previous studies about hail and tornadoes separately, rather than concurrently.
Specific Comments:
- Line 27: The references of Moller et al 1994 and Nelson 1987 are quite old. It would be better to also include some newer references.
- Line 86 “variety of sources”: Please include some examples. Trained spotters? Automated stations?
- Line 88 “Both hail and tornado reports are treated as point events…”: This is an example of a definition that needs further clarification. If the tornado strengthens, or the hail size increases, do you use the maximum or the initial strength/size? If the maximum, is the time and location still counted as the start time?
- Line 88: How does the hail/tornado database determine if reports (especially hail) are continuous or if the hail stopped and started again? I.e. are there MCSs that have multiple hail point events associated with them and if so, is each event distinguished?
- Line 96 “poorly identified”: Consider rewording this statement. This makes it sound like MCSs are rare and hard to detect, which is not the case.
- Line 106 “multiple properties”: Please provide examples if you want to keep this amount of detail (see next comment).
- Line 124 “convective cores defined by…”: Why is the HA2018 method described in such detail if you are using S2017? Please either justify or remove this description.
- Line 135 “maximum radar-MCS boundary”: What is this boundary?
- Line 147 “MCS dataset (hourly): Why is the MCS dataset limited to hourly resolution? Computational limitations? Or is one or more of the components of the dataset produced by others (please make this clearer if this is the case)?
- Line 153 “missing rate”: It’s not clear what you mean by this or why it would decrease with decreasing time.
- Line 166 “within the radar-MCS boundary but outside the MCS-core”: Are these events related to the temporal offset of the hail/tornado and radar observations? I.e the hail or tornado was produced by the core, but the core is moving rapidly enough to not be over this location at the radar-MCS timestamp?
- Line 167 “reports without valid radar coverage”: Does the definition of radar-MCS and the subsequent collocation of the hazard reports to the radar-MCS not already remove these?
- Lines 231-236: Latitude definitions would be helpful here to those not familiar with US geography.
- Line 355-356 “severe hail to significant sever hail”: Please define (or remind of the definition) the sizes for these two categories
Technical Corrections:
- Line 49 “rotate”: rotation
- Line 99 “Erroneous”: erroneous
- Line 169 “sever”: severe
- Line 323 “severe hail event/tornado at”: severe hail event/tornado, respectively, at
- Line 351 “hazard”: hazards
Citation: https://doi.org/10.5194/nhess-2023-16-RC1 -
AC1: 'Reply on RC1', Jingyu Wang, 14 Jun 2023
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2023-16/nhess-2023-16-AC1-supplement.pdf
-
RC2: 'Comment on nhess-2023-16', Anonymous Referee #2, 19 May 2023
This is a nice study that leverages a long-term record of objectively-identified mesoscale convective systems (MCSs) and severe weather reports to identify the extent of hail and tornadoes linked to this storm type. It builds upon past studies on the topic, but is unique in its inclusion of a broader collection of MCS type (most prior studies focus solely on quasi-linear systems). Most of the findings are consistent with prior work, with one exception for the rate of attribution of tornadoes to MCSs with increasing rating/intensity (EF-0 to EF-5). The manuscript is generally well-written and includes appropriate detail on data and methods. The figures are well designed and readable, though the rainbow color ramp used in several of the radar and density figures is not friendly to readers with color-vision deficiency. I have a number of general and specific suggestions for revision, which I outline below.
General Comments
- One opportunity that seems missed, but well within reach of the authors is an attribution study for severe wind reports. Wind is not acknowledged by the authors apart from a brief mention for one of the cases highlighted in Figure 2. I recommend the authors add results for severe wind to their study or at least provide sufficient justification for their exclusion from this analysis.
- The discussion in lines 216-224 conflates documented characteristics of MCS tornado production with interpretation of the hail associations evaluated here. This discussion is confusing and the parallels do not appear to be appropriate to make because the hazard production, its seasonality, etc. are not entirely similar for hail and tornadoes. All discussion of demonstrated tornado linkages should be left to the discussion of the tornado results.
- The discussion in lines 382-389 and 400-402 is too speculative. The limitation that supercells are not identified in the analysis is an important consideration here. Because prior studies focused on MCS/QLCS severe weather attributions have been based on mostly manual evaluation of events with specific avoidance of supercells, the differing result found here may be a direct result of the inclusion of many supercells in your MCS classification. With supercells included, the increase in low-level wind shear in the early evening hours as the GPLLJ is established is also important to tornado production. Thus, I recommend softening some of the speculation here (and perhaps elsewhere) and acknowledging more the potential impact of the inclusion of supercells in your analysis. More specification of the differences between your analysis and prior analyses will also be helpful to making stronger assertions.
- The 27 April 2011 discussions would benefit from citing the recent two-part paper summarizing an in-depth analysis of multiscale aspects of the event: https://doi.org/10.1175/MWR-D-21-0013.1 & https://doi.org/10.1175/MWR-D-21-0014.1
Specific Comments
Lines 17-18: I do not understand what the authors are aiming to communicate with this sentence. Please revise for clarity – perhaps it needs two separate sentence describing findings for hail and tornadoes.
Line 30: “supercell is” should be “supercells are”
Line 48: “such as moist” should be “such as a moist”
Line 49: “rotate” should be “rotation”
Line 56: “tornado” should be “tornadoes”
Line 60: “to the large-scale” should be “to large-scale”
Line 64: “variabilities” should be “variability”
Line 71: “tornado with” should be “tornadoes within”
Line 169: “sever” should be “severe”
Line 187: “more severe tornadoes”. These are all EF0/1. What do you mean by more severe?
Line 192: I recommend noting that such associations are statistically rare. Should cite Trapp et al. 2005 also (https://doi.org/10.1175/WAF-835.1).
Line 225: “because the” should be “because of the”
Line 227: “provides” should be “providing”
Line 228: recommend revising “hot zone” to “maximum frequency”
Line 238: “MCS decrease” should be “MCSs decreases”
Line 240: “reduction of MCS” should be “reduced frequency of MCSs” (I think)
Line 253: recommend revising “hot zone” to “frequency maximum”
Line 352-353: I do not understand what this sentence is aiming to communicate. Please revise for clarity.
Line 353: “tornado” should be “tornadoes”
Line 394: “hails” should be “hail”
Line 396: delete “over the”
Line 413: “tornado” should be “tornadoes”
Line 430: “MCS” should be “MCSs”
Figures 2-4: the colors used for reflectivity/density in these figures are not easily discernable to readers who suffer from color-vision deficiency. Good alternatives are those which are perceptually uniform or divergent. If using Python, there are some good options here: https://matplotlib.org/stable/tutorials/colors/colormaps.html. For radar reflectivity in particular, Spectral is a good choice.
Figure 6: “Normalize” on the x-axes should be “Normalized”
References: several of the citations here are missing DOI numbers. Please double-check for DOIs (even on older articles) and add all that are available.
Citation: https://doi.org/10.5194/nhess-2023-16-RC2 -
AC2: 'Reply on RC2', Jingyu Wang, 14 Jun 2023
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2023-16/nhess-2023-16-AC2-supplement.pdf
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CC1: 'Comment on nhess-2023-16', Andrew Berrington, 23 May 2023
In terms of the percentage of MCS-related tornadoes rated EF2-EF5 in Figure 7 and particularly for violent tornadoes, it has been shown in a number of studies that linear convective systems are not responsible for the vast majority of these events (Trapp et al. 2005, Smith et al. 2012). To observe a 40% fraction of violent tornadoes from MCSs suggests that the separation/delineation/classification between supercells and MCSs needs to be adjusted in this work. In the paragraph mentioning 4/27/2011, where the correct supercellular classification of the afternoon activity by Knupp et al. 2014 is mentioned, a stricter criteria is imposed by the authors that subsequently removes the EF5s from the MCS climatology. Stricter criteria and further quality control, perhaps further involving low-level reflectivity, should be applied to separate tornado cases that are clearly the result of supercells and those with MCSs. While embedded supercells within MCSs can indeed produce very strong tornadoes (e.g. the morning QLCS of 4/27/2011, 2/29/2012 in Harrisburg IL, and 4/13/2020 in Estill SC), the occurrence of these is very infrequent compared to more discrete supercells producing tornadoes of this intensity. While the definition of 'MCS' may include larger complexes including individual supercell storms such as the Feb 2008 case mentioned by the authors – especially using upper level reflectivity or satellite proxies where "connection" of elements may occur – it should be clear that discrete or semi-discrete supercells are a separate storm mode and thus these tornadoes should be classified separately.
References:
Smith, B. T., R. L. Thompson, J. S. Grams, C. Broyles, and H. E. Brooks, 2012: Convective modes for significant severe thunderstorms in the contiguous United States. Part I: Storm classification and climatology. Wea. Forecasting, 27, 1114–1135, https://doi.org/10.1175/WAF-D-11-00115.1.
Trapp, R. J., S. A. Tessendorf, E. S. Godfrey, and H. E. Brooks, 2005: Tornadoes from squall lines and bow echoes. Part I: Climatological distribution. Wea. Forecasting, 20, 23–34, https://doi.org/10.1175/WAF-835.1.
Citation: https://doi.org/10.5194/nhess-2023-16-CC1 -
AC3: 'Reply on CC1', Jingyu Wang, 14 Jun 2023
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2023-16/nhess-2023-16-AC3-supplement.pdf
-
AC3: 'Reply on CC1', Jingyu Wang, 14 Jun 2023
Status: closed
-
RC1: 'Comment on nhess-2023-16', Anonymous Referee #1, 11 May 2023
Review of: “Climatological occurrences of hail and tornado associated with mesoscale convective systems in the United States”
Summary: The authors use collocated ground based radar MCS features and geostationary satellite tracked MCSs to follow MCSs over the United States throughout their lifetimes and define their life stage. Collocated observations of hail and tornadoes are collocated to each MCS to study the climatological occurrence of MCS produced severe hail and tornadoes on a monthly and per lifecycle stage basis. These are also compared with observed hail and tornadoes from all events to determine the percent contribution to the occurrence of these hazards by MCSs. The paper is well written and thorough, and, for the most part, logically organized. It would benefit from clarification of a few points and additional discussion of the methods used. I therefore recommend minor revisions.
General Comments:
- The methods section is lacking in a few key details, mostly descriptions of the datasets. This section should be expanded to include more technical details about how the datasets used are produced and how the derived quantities are defined. Specific examples are provided in the Specific Comments section.
- The introduction feels a bit jumbled and tends to jump from discussing hail to tornadoes and back within the same paragraph. It would read more smoothly and thus make the points of the introduction better if it were reorganized to discuss the findings of previous studies about hail and tornadoes separately, rather than concurrently.
Specific Comments:
- Line 27: The references of Moller et al 1994 and Nelson 1987 are quite old. It would be better to also include some newer references.
- Line 86 “variety of sources”: Please include some examples. Trained spotters? Automated stations?
- Line 88 “Both hail and tornado reports are treated as point events…”: This is an example of a definition that needs further clarification. If the tornado strengthens, or the hail size increases, do you use the maximum or the initial strength/size? If the maximum, is the time and location still counted as the start time?
- Line 88: How does the hail/tornado database determine if reports (especially hail) are continuous or if the hail stopped and started again? I.e. are there MCSs that have multiple hail point events associated with them and if so, is each event distinguished?
- Line 96 “poorly identified”: Consider rewording this statement. This makes it sound like MCSs are rare and hard to detect, which is not the case.
- Line 106 “multiple properties”: Please provide examples if you want to keep this amount of detail (see next comment).
- Line 124 “convective cores defined by…”: Why is the HA2018 method described in such detail if you are using S2017? Please either justify or remove this description.
- Line 135 “maximum radar-MCS boundary”: What is this boundary?
- Line 147 “MCS dataset (hourly): Why is the MCS dataset limited to hourly resolution? Computational limitations? Or is one or more of the components of the dataset produced by others (please make this clearer if this is the case)?
- Line 153 “missing rate”: It’s not clear what you mean by this or why it would decrease with decreasing time.
- Line 166 “within the radar-MCS boundary but outside the MCS-core”: Are these events related to the temporal offset of the hail/tornado and radar observations? I.e the hail or tornado was produced by the core, but the core is moving rapidly enough to not be over this location at the radar-MCS timestamp?
- Line 167 “reports without valid radar coverage”: Does the definition of radar-MCS and the subsequent collocation of the hazard reports to the radar-MCS not already remove these?
- Lines 231-236: Latitude definitions would be helpful here to those not familiar with US geography.
- Line 355-356 “severe hail to significant sever hail”: Please define (or remind of the definition) the sizes for these two categories
Technical Corrections:
- Line 49 “rotate”: rotation
- Line 99 “Erroneous”: erroneous
- Line 169 “sever”: severe
- Line 323 “severe hail event/tornado at”: severe hail event/tornado, respectively, at
- Line 351 “hazard”: hazards
Citation: https://doi.org/10.5194/nhess-2023-16-RC1 -
AC1: 'Reply on RC1', Jingyu Wang, 14 Jun 2023
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2023-16/nhess-2023-16-AC1-supplement.pdf
-
RC2: 'Comment on nhess-2023-16', Anonymous Referee #2, 19 May 2023
This is a nice study that leverages a long-term record of objectively-identified mesoscale convective systems (MCSs) and severe weather reports to identify the extent of hail and tornadoes linked to this storm type. It builds upon past studies on the topic, but is unique in its inclusion of a broader collection of MCS type (most prior studies focus solely on quasi-linear systems). Most of the findings are consistent with prior work, with one exception for the rate of attribution of tornadoes to MCSs with increasing rating/intensity (EF-0 to EF-5). The manuscript is generally well-written and includes appropriate detail on data and methods. The figures are well designed and readable, though the rainbow color ramp used in several of the radar and density figures is not friendly to readers with color-vision deficiency. I have a number of general and specific suggestions for revision, which I outline below.
General Comments
- One opportunity that seems missed, but well within reach of the authors is an attribution study for severe wind reports. Wind is not acknowledged by the authors apart from a brief mention for one of the cases highlighted in Figure 2. I recommend the authors add results for severe wind to their study or at least provide sufficient justification for their exclusion from this analysis.
- The discussion in lines 216-224 conflates documented characteristics of MCS tornado production with interpretation of the hail associations evaluated here. This discussion is confusing and the parallels do not appear to be appropriate to make because the hazard production, its seasonality, etc. are not entirely similar for hail and tornadoes. All discussion of demonstrated tornado linkages should be left to the discussion of the tornado results.
- The discussion in lines 382-389 and 400-402 is too speculative. The limitation that supercells are not identified in the analysis is an important consideration here. Because prior studies focused on MCS/QLCS severe weather attributions have been based on mostly manual evaluation of events with specific avoidance of supercells, the differing result found here may be a direct result of the inclusion of many supercells in your MCS classification. With supercells included, the increase in low-level wind shear in the early evening hours as the GPLLJ is established is also important to tornado production. Thus, I recommend softening some of the speculation here (and perhaps elsewhere) and acknowledging more the potential impact of the inclusion of supercells in your analysis. More specification of the differences between your analysis and prior analyses will also be helpful to making stronger assertions.
- The 27 April 2011 discussions would benefit from citing the recent two-part paper summarizing an in-depth analysis of multiscale aspects of the event: https://doi.org/10.1175/MWR-D-21-0013.1 & https://doi.org/10.1175/MWR-D-21-0014.1
Specific Comments
Lines 17-18: I do not understand what the authors are aiming to communicate with this sentence. Please revise for clarity – perhaps it needs two separate sentence describing findings for hail and tornadoes.
Line 30: “supercell is” should be “supercells are”
Line 48: “such as moist” should be “such as a moist”
Line 49: “rotate” should be “rotation”
Line 56: “tornado” should be “tornadoes”
Line 60: “to the large-scale” should be “to large-scale”
Line 64: “variabilities” should be “variability”
Line 71: “tornado with” should be “tornadoes within”
Line 169: “sever” should be “severe”
Line 187: “more severe tornadoes”. These are all EF0/1. What do you mean by more severe?
Line 192: I recommend noting that such associations are statistically rare. Should cite Trapp et al. 2005 also (https://doi.org/10.1175/WAF-835.1).
Line 225: “because the” should be “because of the”
Line 227: “provides” should be “providing”
Line 228: recommend revising “hot zone” to “maximum frequency”
Line 238: “MCS decrease” should be “MCSs decreases”
Line 240: “reduction of MCS” should be “reduced frequency of MCSs” (I think)
Line 253: recommend revising “hot zone” to “frequency maximum”
Line 352-353: I do not understand what this sentence is aiming to communicate. Please revise for clarity.
Line 353: “tornado” should be “tornadoes”
Line 394: “hails” should be “hail”
Line 396: delete “over the”
Line 413: “tornado” should be “tornadoes”
Line 430: “MCS” should be “MCSs”
Figures 2-4: the colors used for reflectivity/density in these figures are not easily discernable to readers who suffer from color-vision deficiency. Good alternatives are those which are perceptually uniform or divergent. If using Python, there are some good options here: https://matplotlib.org/stable/tutorials/colors/colormaps.html. For radar reflectivity in particular, Spectral is a good choice.
Figure 6: “Normalize” on the x-axes should be “Normalized”
References: several of the citations here are missing DOI numbers. Please double-check for DOIs (even on older articles) and add all that are available.
Citation: https://doi.org/10.5194/nhess-2023-16-RC2 -
AC2: 'Reply on RC2', Jingyu Wang, 14 Jun 2023
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2023-16/nhess-2023-16-AC2-supplement.pdf
-
CC1: 'Comment on nhess-2023-16', Andrew Berrington, 23 May 2023
In terms of the percentage of MCS-related tornadoes rated EF2-EF5 in Figure 7 and particularly for violent tornadoes, it has been shown in a number of studies that linear convective systems are not responsible for the vast majority of these events (Trapp et al. 2005, Smith et al. 2012). To observe a 40% fraction of violent tornadoes from MCSs suggests that the separation/delineation/classification between supercells and MCSs needs to be adjusted in this work. In the paragraph mentioning 4/27/2011, where the correct supercellular classification of the afternoon activity by Knupp et al. 2014 is mentioned, a stricter criteria is imposed by the authors that subsequently removes the EF5s from the MCS climatology. Stricter criteria and further quality control, perhaps further involving low-level reflectivity, should be applied to separate tornado cases that are clearly the result of supercells and those with MCSs. While embedded supercells within MCSs can indeed produce very strong tornadoes (e.g. the morning QLCS of 4/27/2011, 2/29/2012 in Harrisburg IL, and 4/13/2020 in Estill SC), the occurrence of these is very infrequent compared to more discrete supercells producing tornadoes of this intensity. While the definition of 'MCS' may include larger complexes including individual supercell storms such as the Feb 2008 case mentioned by the authors – especially using upper level reflectivity or satellite proxies where "connection" of elements may occur – it should be clear that discrete or semi-discrete supercells are a separate storm mode and thus these tornadoes should be classified separately.
References:
Smith, B. T., R. L. Thompson, J. S. Grams, C. Broyles, and H. E. Brooks, 2012: Convective modes for significant severe thunderstorms in the contiguous United States. Part I: Storm classification and climatology. Wea. Forecasting, 27, 1114–1135, https://doi.org/10.1175/WAF-D-11-00115.1.
Trapp, R. J., S. A. Tessendorf, E. S. Godfrey, and H. E. Brooks, 2005: Tornadoes from squall lines and bow echoes. Part I: Climatological distribution. Wea. Forecasting, 20, 23–34, https://doi.org/10.1175/WAF-835.1.
Citation: https://doi.org/10.5194/nhess-2023-16-CC1 -
AC3: 'Reply on CC1', Jingyu Wang, 14 Jun 2023
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2023-16/nhess-2023-16-AC3-supplement.pdf
-
AC3: 'Reply on CC1', Jingyu Wang, 14 Jun 2023
Jingyu Wang et al.
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